cmd/compile: prevent typecheck importer reading type parameter twice

This is a port of CL 349009 to typecheck importer.

Fixes #48306

Change-Id: Iec3f078089346bd85f0ab739896e079940325011
Reviewed-on: https://go-review.googlesource.com/c/go/+/349011
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

3 files changed, 31 insertions, 0 deletions

diff --git a/test/typeparam/issue48306.dir/a.go b/test/typeparam/issue48306.dir/a.go
new file mode 100644
index 0000000000..739750b20b
--- /dev/null
+++ b/test/typeparam/issue48306.dir/a.go
@@ -0,0 +1,9 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package a
+
+type I[T I[T]] interface {
+	F() T
+}
diff --git a/test/typeparam/issue48306.dir/main.go b/test/typeparam/issue48306.dir/main.go
new file mode 100644
index 0000000000..5d602fe07c
--- /dev/null
+++ b/test/typeparam/issue48306.dir/main.go
@@ -0,0 +1,15 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "a"
+
+type S struct{}
+
+func (*S) F() *S { return nil }
+
+func main() {
+	var _ a.I[*S] = &S{}
+}
diff --git a/test/typeparam/issue48306.go b/test/typeparam/issue48306.go
new file mode 100644
index 0000000000..76930e5e4f
--- /dev/null
+++ b/test/typeparam/issue48306.go
@@ -0,0 +1,7 @@
+// rundir -G=3
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ignored